Molecular beam epitaxy as a growth technique for achieving free-standing zinc-blende GaN and wurtzite AlxGa1-xN
In this study we have used plasma-assisted molecular beam epitaxy (PA-MBE) and have produced for the first time free-standing layers of zinc-blende GaN up to 100μm in thickness and up to 3-inch in diameter. We have shown that our newly developed PA-MBE process for the growth of zinc-blende GaN layers can also be used to achieve free-standing wurtzite AlxGa1-xN wafers. Zinc-blende and wurtzite AlxGa1-xN polytypes can be grown on different orientations of GaAs substrates - (001) and (111)B respectively. We have subsequently removed the GaAs using a chemical etch in order to produce free-standing GaN and AlxGa1-xN wafers. At a thickness of ∼30µm, free-standing GaN and AlxGa1-xN wafers can easily be handled without cracking. Therefore, free-standing GaN and AlxGa1-xN wafers with thicknesses in the 30–100μm range may be used as substrates for further growth of GaN and AlxGa1-xN-based structures and devices. We have compared different RF nitrogen plasma sources for the growth of thick nitride AlxGa1-xN films including a standard HD25 source from Oxford Applied Research and a novel high efficiency source from Riber. We have investigated a wide range of the growth rates from 0.2 to 3µm/h. The use of highly efficient nitrogen RF plasma sources makes PA-MBE a potentially viable commercial process, since free-standing films can be achieved in a single day. Our results have demonstrated that MBE may be competitive with the other group III-nitrides bulk growth ...
This report continues the development of ALIs as a clinical tool in wildlife while systematically testing one possible method for determining an optimal ALI for a particular species. PMID: 32228119 [PubMed - as supplied by publisher]
Authors: Park J, Kim J, Chen Y, Song HC, Chen Y, Zheng M, Surh YJ, Kim UH, Park JW, Joe Y, Chung HT Abstract Oxidative stress is recognised as a key factor that can lead to cellular senescence and aging. Carbon monoxide (CO) is produced by haemoxygenase-1 (HO-1), which exerts cytoprotective effects in aging-related diseases, whereas the effect of CO on cellular senescence and aging has not been elucidated. In the current study, we clearly demonstrated that CO delays the process of cellular senescence and aging through regulation of miR-34a and Sirt1 expression. CO reduced H2O2-induced premature senescence in human ...
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